Anodized Aluminum Alloy Research Articles

Effects of hard anodizing on mechanical and electrochemical characteristics of aluminum alloys under tribocorrosion condition

In this research, the effects of hard anodizing on the mechanical and electrochemical characteristics of aluminum alloys under tribocorrosion conditions was investigated. Compared with dry conditions, friction coefficient of aluminum alloys under tribocorrosion conditions increased, whereas that of hard anodized specimens decreased. This was attributed to corrosive ions in the solution corroding the transfer film of the counter-body and tribofilm of the hard anodized specimen. In potentiodynamic polarization experiments under tribocorrosion conditions, the aluminum alloys exhibited high current density with applied load. However, at potentials above –0.05 V, current density decreased and was reversed. This is believed to be due to the corrosive ions preferentially reacting with the generated wear debris, thereby reducing the oxidation reaction with wear track. However, the current density of the hard anodized specimens increased with load and potential. In addition, the increasing rate in the wear width and depth was significant under tribocorrosion conditions (Width: 42.65 %, Depth: 32.63 %). This is due to the cavitation and fluid impact generated during friction/wear accelerating the cracking and damage of the hard anodizing film with the brittleness and porousity. However, the tribocorrosion resistance of the hard anodized aluminum alloy was improved by more than 97 %.

Interfacial structure and properties of anodized 6061 Al alloy joints by ultrasonic-assisted hot dipping and soldering using a Sn–9Zn–2Al filler metal

Al alloy joints soldered with Sn-based filler metal are susceptible to corrosion and early failure when exposed to moisture, resulting in severe accidents and substantial economic losses. This study proposes a method to prevent galvanic corrosion by separating Al alloys and Sn-based filler metals with an insulating barrier layer of anodized aluminum oxide (AAO) composed of Al2O3. The successful joining of anodized aluminum alloy (AAA) with Sn–9Zn–2Al was achieved through ultrasonic-assisted hot dipping and soldering in air at 240 °C. Microstructural examination revealed strong bonding between the solder alloy and AAO, with the solder infiltrating the AAO nanotubes and a transition layer consisting of two sublayers at the interface: amorphous ZnO mixed with nanocrystals (ZnO and Al2O3) and amorphous Al2O3. The shear strength of the joints ranged from 31.8 to 32.8 MPa when subjected to ultrasonic hot dipping for 0.5–2.0 s, with no significant difference observed. Fracture initiation and propagation occur within the transition layer at the interface. The shear strength of joints subjected to dipping for more than 3.0 s decreased slightly to 27.9 MPa due to localized peeling off of AAO from the Al substrate. The formation of the interface involves the segregation of Al and Zn on the liquid filler metal surface, driven by differences in atomic activity. Due to the jet force from cavitation, an Al-rich liquid infiltrates the nanotube, resulting in the formation of Zn–O at the interface and Al–O both at the interface and within the nanotube. Throughout this process, the wetting model shifts from a Cassie state to a near-Wenzel state. Immersion tests of two types of joints, Al/SnZnAl/Al and AAA/SnZnAl/AAA, confirmed that galvanic corrosion of Sn/Al was completely inhibited by the latter. Consequently, AAA joints demonstrate excellent corrosion resistance, validating this approach as a promising solution to the Al/Sn galvanic corrosion issue.

Critical Challenges in the Anodizing Process of Aluminium–Silicon Cast Alloys—A Review

The microstructure of the substrate plays a crucial role in the anodizing process. Anodizing cast aluminum alloys is quite challenging due to the higher levels of alloying elements present compared to pure aluminum. Elements such as silicon, iron, and copper significantly impact the growth and quality of the anodic layer. Additionally, anodizing parameters such as electrolyte composition, current density, and temperature are critical in determining the morphology and thickness of the anodic film. The casting process, surface condition, and post-treatment also affect the properties of the anodic layer. Optimizing these parameters is essential to achieve a durable and high-quality anodic layer. This work aims to provide a comprehensive understanding of the various factors affecting the anodizing of cast aluminum alloys and the properties of the anodic layer, including its thickness, corrosion resistance, and wear resistance.

Structure and properties of the hot pressing molded anodized aluminum alloy/polyformaldehyde hybrids

The metal-plastic hybrid is one of the important solutions for lightweight and high-strength composite. The anodized aluminum alloy（AAA）/polyformaldehyde（POM） hybrids with excellent mechanical properties were processed by the hot pressing technology. The surface of the aluminum alloy plate was firstly pretreated with phosphoric acid and oxalic acid anodizing, resulting in a large number of micro-nano scale pores on the surface. These pores were well embedded with plastic melt during hot pressing to form micro-nano mechanical interlocking structures and the Al–O–C chemical bond at the interface is generated, thus ensuring good bonding strength at the metal and plastic interface. The maximum tensile-shear strength of the metal-plastic hybrid was 30.65 MPa, meanwhile, the metal-plastic interface failure presented mainly a mixed failure mode, including resin removal from the metal surface and plastic tearing from the plastic surface. At the same time, the salt spray test, thermal shock test, and variable temperature test were adopted to investigate the application performance of the metal-plastic hybrid. The Al/POM hybrids were able to maintain their mechanical strength above 20 MPa for 28 days in a salt spray environment, 14 times in a thermal shock cycle, and at high temperatures. The high mechanical strength of hybrid has good potential for automotive applications.

Corrosion failure analysis and solutions of aluminum alloy gas path plate used in sanding device of high-speed train

During the maintenance of a high-speed train, it was frequently found that the anodized aluminum alloy gas path plates in the sanding device had different degrees of corrosion. In this paper, SEM, EDS, XRD and LAD-EDTEST spectrometer were used to analyze the macro and micro morphology, elements and phases of corrosion product, element compositions of the matrix and assembly problem of the gas path plates. The mechanism of delamination spalling corrosion caused by local pitting corrosion of anodized aluminum alloy gas path plate was described. In addition, the properties of the coatings produced by different surface treatment methods and different substrate materials were compared. The test results indicate that the corrosion protection level of the micro-arc oxide coating is higher than that of the anodic oxide coating, which is mainly composed of γ-Al2O3 and contains a certain amount of α-Al2O3. Compared with 2A12-T4 aluminum alloy, the micro arc oxidation (MAO) coating of 6082-T6 aluminum alloy has lower porosity, higher hardness, higher corrosion potential, lower corrosion current, and better corrosion resistance, and 6082-T6 aluminum alloy is more suitable for use as the gas plate material. Meanwhile, it is proposed that the MAO coating with 35 μm can obviously improve the corrosion resistance of the gas path plate.

Micro-alloyed aluminium alloys as anodes for aluminium-air batteries with a neutral electrolyte

Aluminium (Al)-air batteries possess a low cost, high theoretical capacity, efficiency, and good recyclability. However, aluminium metal, as the anode material, suffers from low anodic efficiency and limited battery storage life. In this study, three extruded micro-alloyed Al alloys (Al-0.1Fe-0.3Si, Al-0.2Fe-0.2Si, and Al-0.2Fe-0.8Si) were investigated as anode materials for Al-air batteries in a neutral electrolyte. These three alloy anodes were also discharged in an alkaline electrolyte for comparison purposes. The results indicate that the micro-alloying elements Fe and Si accelerate corrosion in a neutral electrolyte. The composition of Fe and Si micro-alloying adversely affects the anodic performance of Al-air batteries but benefits the electrochemical activity of the aluminium substrate. In alkaline electrolytes, aluminium alloy anodes suffer severe self-corrosion and exhibit low anodic efficiency. Additionally, Al-0.1Fe-0.3Si and Al-0.2Fe-0.2Si alloys exhibit better battery performance than Al-0.2Fe-0.8Si at the current densities <10 mA·cm−2 in a neutral electrolyte.

Chromium/nickel-free conversion coating as cold post-treatment to anodized AA2024-T3 for corrosion resistance increase

The AA2024-T3 alloy exhibits significant properties for industrial applications, including low weight and high mechanical strength. However, its susceptibility to corrosion, attributed to precipitation hardening, requires effective surface treatments. Anodized aluminum alloys offer a robust protective structure; nevertheless, their porous layer must enable the anchoring of an additional coating or be adequately sealed. Boiling water sealing, though a non-toxic process, demands substantial energy consumption, while toxicity concerns limit the use of sealing with dichromate and Ni salts. Consequently, there is a pressing need to explore novel sealing methods capable of operating at lower temperatures for brief durations without Cr(VI) or Ni. This study proposes an alternative post-treatment for AA2024-T3 anodic layers generated in tartaric sulfuric acid (TSA). The method involves immersing the samples for 5 min in solutions containing H2ZrF6 alone, Na2MoO4 with KMnO4, and a combination of all three. The resulting layers underwent analysis using scanning electron microscopy (SEM), energy dispersion X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), open circuit potential (OCP) measurements during coating deposition, electrochemical impedance spectroscopy (EIS), and a visual examination post-immersion in a NaCl solution. The findings indicate that the Zr and Zr-Mo-Mn conversion coatings partially sealed the porous structure of the anodic oxide film, thereby enhancing its corrosion resistance in chloride medium. The incorporation of molybdate and permanganate ions intensified the precipitation of Zr oxide-fluorides within and on the porous layer, leading to improved corrosion resistance of the anodized alloy compared to Zr-only coating.

Synergistic Effect of Anodic Hydrophilic and Hydrophobic Interfaces for Long Cycle Life Aqueous Aluminum–Zinc Hybrid Ion Batteries

AbstractAqueous aluminum ion batteries (AAIBs) have drawn considerable attention due to their intrinsic safety, cost‐effectiveness, eco‐friendliness, and high theoretical capacity of aluminum. Currently, suitable anode materials are crucial for the development of high‐performance AAIBs. For the first time, a hydrophilic (ZnCr2O4) and hydrophobic (PVDF) layer modified zinc anode paired with an aluminum‐based aqueous electrolyte to construct a high‐performance aluminum–zinc hybrid ion battery. The Hydrophilic ZnCr2O4 layer of anode endows the battery with low polarization by boosting the pre‐desolvation and deposition kinetics of aluminum/zinc ions. Meanwhile, the hydrophobic PVDF layer suppresses water‐induced corrosion of the anode. The synergistic effect of the hydrophilic and hydrophobic layers of the anode stimulates the battery to exhibit unprecedented cycle life (&gt; 6000 cycles) and considerable discharge capacity (280 mAh g−1), compared to the batteries proposed in previous works paired with aluminum alloy anodes and aluminum‐based aqueous electrolytes. This novel anode provides powerful backing for the development of long‐life and high‐capacity aqueous polyvalent ion batteries due to its low cost and simple fabrication process.

Investigations on Mn shielding the negative effect of Fe in the aluminum alloy anodes used for Al-air batteries

Investigations on Mn shielding the negative effect of Fe in the aluminum alloy anodes used for Al-air batteries

Lithium salt post-treatment of anodized 7075-T6 alloy for enhancing corrosion resistance in neutral and acidified NaCl environment

An anodized 7075-T6 aluminum alloy was post-treated in three different lithium salt solutions (Li2CO3, Li2C2O4 or LiNO3) under optimized conditions, respectively, in order to improve corrosion resistance of the alloy in both neutral NaCl (0.05 M, pH = 6.5) and acidified NaCl (0.6 M, pH = 3.5) solutions. The results indicate that the porous anodic film can be effectively sealed by the post-treatment and the sealing products are a mixture of boehmite, Li–Al amorphous hydroxides and Li–Al-LDH, with the relative proportion of each component varying with the sealing conditions. All lithium salt treated alloy specimens passed 1100 h of neutral salt spray test, and the Li2C2O4-based alloy specimen exhibited higher corrosion resistance than others in the neutral NaCl environment. Although the corrosion resistance of the coating deteriorated in the acidified NaCl solution, the lithium salt treated alloy specimens still showed distinct advantage over the hot water sealed counterpart, especially for the LiNO3-based process.

Effects of flocculant and corrosion inhibitor compounding on the electrochemical corrosion behavior of the anode in Al-air batteries

To solve the problem of precipitates affecting battery performance in aluminum-air batteries. This study employed a variety of techniques—including flocculant-simulated sedimentation experiments, electrochemical assays, constant current discharge tests, and microscopic morphology assessments—to evaluate the synergistic effects of corrosion inhibitors and flocculants in the electrolyte of aluminum-air batteries. The inorganic polymer compound polyalumi rlillm sulfate (PSA) and the inorganic compound aluminum sulfate were investigated in a 4 mol/L NaOH+ 0.06 mol/L Na2SnO3 solution to elucidate the electrochemical corrosion mechanism of the 5052 aluminum alloy anode, as well as the sedimentation time and effect of colloidal precipitation. The results showed that the compounding of the two flocculants with the conventional corrosion inhibitor Na2SnO3 enhanced both the sedimentation rate of aluminum hydroxide in alkaline media and decreased the corrosion rate of the aluminum anode. Specifically, 3 g/L PSA was found to be most efficacious, elevating the sedimentation efficiency by 70.6%. Additionally, 1 g/L PSA demonstrated the most significant inhibitory effect on the self-corrosion of 5052 aluminum alloy, leading to an increase in the anode battery's capacity density by 15.5–35.1%. The synergistic action of flocculants and corrosion inhibitors chiefly accelerated the sedimentation rate of precipitates, maintained electrolyte conductivity, and facilitated the formation of a protective film on the surface of the aluminum anode to reduce the self-corrosion rate of aluminum, thereby promoting the improvement of discharge performance of aluminum-air batteries.

An assessment of pitting corrosion in anodized aluminum alloys: It might not be what it seems

AbstractIn this study, special attention was given to the characterization of pits on the anodized aluminum alloy (Al–Zn–Mg–Cu) with an anodic aluminum oxide formed in tartaric sulfuric acid. Anodic polarization in 0.1 mol L−1 NaCl solution was used to initiate pitting corrosion in the anodized alloy. Pit characteristics, such as morphology and depth, were evaluated by using optical microscopy and optical profilometry, and scanning electron microscopy. The methodology adopted in this study revealed severe under‐film pitting due to highly occluded conditions and showed that the extent of the under‐film pitting is significantly greater than the size of pit mouth observed from the surface.

Study on effect of injection temperature on shear strength of the direct bond between polyphenylene sulfide and anodized aluminum alloy

A simple and environmentally friendly technique has been proposed to form a composite structure of high interfacial bonding strength between polyphenylene sulfide (PPS) and aluminum alloy (Al). The Al substrate is modified through anodization and enlarging treatments. The influences of injection temperature on the anodic aluminum oxide film surface on the interfacial bond strength of the formed PPS-Al is discussed. The results revealed that when the injection temperature of PPS was set at 310°C, the bonding strength increased to 18.0 MPa. The adhesive strength exhibits a clear dependency on the injection temperature. At higher injection temperatures, PPS exhibits higher flowability and better penetration into nanoscale pores, resulting in a strong interlocking between PPS and anodized aluminum alloy.

Material characterisation of anodising effects on small fatigue crack nucleation in AA7XXX alloys

The precursor cleaning steps in the anodising surface finish process for aluminium alloy aircraft parts are known to lead to etching of surface-breaking intermetallic particles and grain boundaries, which in turn leads to preferential sites for fatigue crack nucleation. Type 1C anodising per MIL-A-8625F, is a favoured aircraft aluminium part corrosion protection treatment meeting modern health and environmental requirements. Type 1C anodising uses electrolysis in a non-chromic acid bath (typically based on sulphuric, boric-sulphuric or phosphoric acid formulations) to develop a thick aluminium oxide surface layer. In previous studies the equivalent initial damage sizes of these nucleation sites was calculated from near surface fatigue crack growth measurements using quantitative fractography in both Type 1C anodised aluminium alloy 7050-T7451 and 7085-T7452. A notable difference was observed in the values for these two materials with AA7085-T7452 equivalent initial damage sizes being significantly smaller. Since these values are critical crack starting size assumptions in fatigue life analysis for aircraft fleets, the observed differences must be investigated and explained for notionally similar alloys under identical conditions.In this work, the material surrounding the population of crack nucleation sites in several Type 1C anodised fatigue tested specimens manufactured from AA7050-T7451 and AA7085-T7452 materials has been characterised using precise surface preparation methods and scanning electron microscopy techniques. It has been demonstrated that there is a statistically significant difference in the number, size, aspect ratio and distribution of surface breaking Al7Cu2Fe intermetallic particles beneath the anodising layer that, when etched out during the anodising process, are responsible for fatigue crack nucleation in 7050-T7451 over 7085-T7452 material. The increased size, angular shape and coverage of these intermetallics in AA7050 serves to increase their effectiveness as preferential locations for fatigue crack nucleation through two mechanisms, as a highly localised stress concentrating feature, as well as through their ability to sample more of the material's microstructural features ensuring a discontinuity is present in the most favourable orientation and location for fatigue crack nucleation.

Influence of pre-treatments on adhesion, barrier and mechanical properties of epoxy coatings: A comparison between steel, AA7075 and AA2024

In this work five independent pre-treatments – mechanical polishing, alkaline and acid etching, sol-gel primer, and anodizing – were applied on mild steel and aluminum (AA7075 and AA2024) substrates before the deposition of epoxy coatings. The results demonstrate that efficient adhesion can be achieved by simple methodologies and widely available chemicals as an alternative to toxic conversion layers or highly energetic processes. All the treatments provided higher adhesion (up to 75%, 61% and 14% on AA7075, AA2024 and steel, respectively) and better anti-corrosion performance (increase of impedance values at low frequency up to four orders of magnitude) than the polished reference. The anodizing of aluminum alloys yielded good anti-corrosion performance, but slightly lower mechanical properties compared to sol-gel primer and alkaline etching. The hydroxyls density was found to play a major role in strong adhesion prevailing over surface roughness, contact area, oxide thickness and hydrophobicity. Despite the efficient performance of hydrogen bonds from acid and alkaline etching on aluminum, these connections do not yield sufficiently stable bonds that make an impermeable barrier of epoxy coatings on steel. Covalent bonds (Me-O-Si) represent the key to achieve a significant improvement in mechanical and chemical resistance against the ingress of water and polymer chain relaxation. This makes the sol-gel primer a simple, economical, and environmentally alternative towards efficient bonding at a molecular level.

The Influence of the Structure of Azo Compounds on the Deposition Process and the Quality of Copper Coatings on Anodized Aluminum Alloys

The Influence of the Structure of Azo Compounds on the Deposition Process and the Quality of Copper Coatings on Anodized Aluminum Alloys

Investigation on anodized 5052 aluminum alloy and its corrosion resistance in simulated acid rain

5052 Al alloy commonly used for construction structures was anodized from the mixed acid electrolyte of citric acid and sulfuric acid to further improve the durability of Al alloy construction components. Different anodized aluminum alloys were prepared by changing the concentration of citric acid in the electrolyte. The surface morphology, structure, thickness and corrosion resistance of the anodized aluminum alloys were characterized and analyzed. The results show that adding appropriate amount of citric acid has a certain corrosion inhibition effect, which reduces the corrosion dissolution degree of the anodized aluminum alloy. At the same time, adding appropriate amount of citric acid in the electrolyte is beneficial to increase the thickness of anodized aluminum alloy, resulting in the enhancement of corrosion resistance in simulated acid rain. When the concentration of citric acid in the electrolyte is 70 g/L, the anodized aluminum alloy is uniform with higher thickness and better corrosion resistance in simulated acid rain.

Effect of silane surface modification on the bonding properties of the hot-pressing molded polycarbonate/aluminum alloy hybrid

Ultrasonic-assisted hot-pressing molding was employed to produce the plastic-metal samples to examine how the silane coupling agent affected the bonding properties of the polycarbonate/aluminum alloy hybrid. With the application of the ultrasonic field, the tensile shear strength rose. Scanning electron microscopy was utilized to examine the bonding layer of the polycarbonate/aluminum hybrid, which establishes its morphology structure. The results indicated that a mechanical interlocking structure was generated via the plastic encased in nanopores on the aluminum alloy surface. Furthermore, X-ray photoelectron spectroscopy indicated that the bonding layer was strongly connected due to the chemical bonding interactions between the Al-O-Si and (C=O)-NH groups. Specifically, the tensile shear strength of the polycarbonate/aluminum alloy hybrid reached 10.6 MPa under mechanical interlocking after the aluminum alloy was anodized with a 10% mass fraction of phosphoric acid solution. Then, after treatment with a 4% volume fraction silane coupling agent on the anodized aluminum alloy surface, the tensile shear strength of the polycarbonate/aluminum alloy hybrid reached 17.8 MPa under the combined effect of mechanical interlocking and chemical bonding, which was increased by 67.9% compared with the sample without silane coupling agent. The results indicate that the use of a silane coupling agent can effectively improve the tensile shear strength of polycarbonate/aluminum alloy hybrid.

Effect of microwave melting and subsequent rolling on the corrosion behavior and electrochemical properties of an aluminum anode using response surface methodology

To obtain aluminum-air batteries with a high anodic efficiency and low corrosion rate, it is necessary to study the methods by which their aluminum alloy anodes are prepared. Here, the performance of an aluminum alloy anode was optimized by microwave melting and rolling. The aluminum anode showed the best performance under a 1000 W microwave power, two passes, and 40% reduction degree (sample denoted 1000W-2–40%). Under these conditions, the grain size of the Al–Zn–Bi–Pb anode was uniform, and no intergranular corrosion was observed. The corrosion resistance was high, and the anodic efficiency reached 72.72%. Finally, by observing the microstructure of an aluminum anode obtained under 1000 W microwave treatment, the corrosion mechanism was analyzed. The activity of the rolled aluminum anode was improved due to the existence of ZnAl2O4 phase. However, in 1000W-1–30%, 1000W-2–20%, and 1000W-3–30% samples, fine grains precipitated at high-angle grain boundaries. The grain orientation was mainly (110), which led to the intergranular corrosion of a large area of the anode, which made it unsuitable for use in aluminum-air batteries.

Investigation on the Effect of a Chromium-Free Sealing Treatment for the Corrosion Resistance of AA2198-T851 after Tartaric Sulphuric Anodizing (TSA)

The AA 2198-T851 is a third-generation Al-Li alloy developed for use in the aircraft industry. Al-Li alloys are susceptible to localized corrosion due to their complex microstructure resulting from the used thermomechanical treatment. In order to prevent localized corrosion, these alloys are usually protected by anodizing in order to avoid a corrosive environment. Subsequently, for anodizing, a sealing treatment is usually performed for parts. Some sealing treatments use hexavalent-chromium-ion-containing solutions. In this investigation, a chromium-free sealing treatment in a solution with cerium ions has been carried out, and the effect on the corrosion resistance of the AA2198-T851 alloy was investigated. Hydrothermally sealed or unsealed samples were also tested for corrosion resistance for comparison reasons. The corrosion resistance of the anodized aluminum alloy, either hydrothermally sealed or in a cerium-ion-containing solution, was evaluated in a sodium chloride solution by electrochemical impedance spectroscopy as a function of immersion time. The samples sealed in a cerium-containing solution increased their corrosion resistance when compared to the hydrothermally sealed. The effectiveness of the sealing process with cerium that was observed in the electrochemical tests indicated that after the corrosive attack of the barrier layer, there was a “sealing” process of the sample surface.